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Abstract. Mixed-layer depth (MLD) exhibits significant variability, which is important for atmosphere–ocean exchanges of heat and atmospheric gases. The origins of the mesoscale MLD variability in the Southern Ocean are studied here in an idealised regional ocean–atmosphere model (ROAM). The main conclusion from the analysis of the upper-ocean buoyancy budget is that, while the atmospheric forcing and oceanic vertical mixing, on average, induce the mesoscale variability of MLD, the three-dimensional oceanic advection of buoyancy counteracts and partially balances these atmosphere-induced vertical processes. The relative importance of advection changes with both season and average MLD. From January to May, when the mixed layer is shallow, the atmospheric forcing and oceanic mixing are the most important processes, with the advection playing a secondary role. From June to December, when the mixed layer is deep, both atmospheric forcing and oceanic advection are equally important in driving the MLD variability. Importantly, buoyancy advection by mesoscale ocean current anomalies can lead to both local shoaling and deepening of the mixed layer. The role of the atmospheric forcing is then directly addressed by two sensitivity experiments in which the mesoscale variability is removed from the atmosphere–ocean heat and momentum fluxes. The findings confirm that mesoscale atmospheric forcing predominantly controls MLD variability in summer and that intrinsic oceanic variability and surface forcing are equally important in winter. As a result, MLD variance increases when mesoscale anomalies in atmospheric fluxes are removed in winter, and oceanic advection becomes a dominant player in the buoyancy budget. This study highlights the importance of oceanic advection and intrinsic ocean dynamics in driving mesoscale MLD variability and underscores the importance of MLD in modulating the effects of advection on upper-ocean dynamics.
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The Moist Quasi-Geostrophic Coupled Model: MQ-GCM 2.0
Abstract. This paper contains a description of recent changes tothe formulation and numerical implementation of the Quasi-GeostrophicCoupled Model (Q-GCM), which constitute a major update of the previousversion of the model (Hogg et al., 2014). The Q-GCM model has been designedto provide an efficient numerical tool to study the dynamics of multi-scalemidlatitude air–sea interactions and their climatic impacts. The presentadditions/alterations were motivated by an inquiry into the dynamics ofmesoscale ocean–atmosphere coupling and, in particular, by an apparent lackof the Q-GCM atmosphere's sensitivity to mesoscale sea-surface temperature (SST)anomalies, even at high (mesoscale) atmospheric resolutions, contrary toample theoretical and observational evidence otherwise. Major modificationsaimed at alleviating this problem include an improved radiative-convectivescheme resulting in a more realistic model mean state and associated modelparameters; a new formulation of entrainment in the atmosphere, whichprompts more efficient communication between the atmospheric mixed layer andfree troposphere; and an addition of a temperature-dependent windcomponent in the atmospheric mixed layer and the resulting mesoscalefeedbacks. The most drastic change is, however, the inclusion of moistdynamics in the model, which may be key to midlatitude ocean–atmospherecoupling. Accordingly, this version of the model is to be referred to as theMQ-GCM model. Overall, the MQ-GCM model is shown to exhibit a rich spectrumof behaviors reminiscent of many of the observed properties of the Earth'sclimate system. It remains to be seen whether the added processes are ableto affect in fundamental ways the simulated dynamics of the midlatitudeocean–atmosphere system's coupled decadal variability.
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- Award ID(s):
- 1941963
- PAR ID:
- 10457357
- Date Published:
- Journal Name:
- Geoscientific Model Development
- Volume:
- 15
- Issue:
- 19
- ISSN:
- 1991-9603
- Page Range / eLocation ID:
- 7449 to 7469
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.5194/gmd-15-7449-2022
